A 44-year-old man presented with an exophytic papillomatous growth in the tarsal conjunctiva of his right eye. The tumour was excised and subjected to histological examination. On light microscopy, a squamous cell papilloma without signs of dysplasia was disclosed, because the entire tissue block was cut into sections, the performance of a conventional in situ hybridization for detection of human papillomavirus (HPV) DNA was not possible. An alternative approach was used to demonstrate the presence of HPV 11 DNA in the papilloma. The cover slip was removed. The individual van Gieson-stained sections on the (routine, uncoated) slides were cut apart by glass knife, and mounted (still attached on the original slide) separately on new microscopy slides. These slides were subjected to in situ DNA hybridization with biotin-labelled DNA probes of HPV 6, 11, 16, and 18, under conditions of high stringency (Tm-17 degrees C). Special caution was taken to prevent the detachment of sections. The papilloma displayed positive hybridization with the HPV-II probe, the intense signals being localized on the nuclei of koilocytotic cells. Infection with HPV-6 (or the closely related HPV-11) appears to be responsible for the majority of the conjunctival papillomas of children and young adults reported so far. The presence of genital tract HPV types 6/11 in these lesions suggests that some of the infections might have been acquired during the passage through an infected birth canal. The presence of HPV 6/11 in adult conjunctival papillomas might reflect a) an activation of a latent infection acquired as above, or b) a new infection transmitted from other mucosal sites, the genital tract included. The role of HPV in conjunctival dysplasias and malignant transformation is not clear as yet.